Efforts to describe cephalometric data more efficiently involve abstracting closed curves through the use of a new geometry of form. The rationale is based on the observation that many biologically derived shapes are characterized by incremental development along discrete boundaries. Analysis of such shapes in terms of axes of symmetry determined by the centers of inscribed discs plus the associated radii permits unequivocal bases for segmental description which can be reversibly related to specific areas of diagnostic interest. This results in a new quasi-topological basis for subsequent analysis and description. As such it yields discrete measures (branch points, angles, etc.) which can be used as intrinsically derived fiducial references. Preliminary analyses of computer derived symmetric axes suggest that these measures are particularly well suited to longitudinal assessment of growth patterns derived from cephalometric data. BIBLIOGRAPHIC REFERENCES: Nagel, R.N. and Blum, H.: A Symmetric Axis Basis for Object Recognition and Description. Proc. of the 1976 IEEE Conference on Decision and Control, WA-4, 168-170, 1976. Blum, H. and Nagel, R.N.: Shape Description Using Weighted Symmetric Axis Features. Proc. of IEEE Computer Society Conference on Pattern Recognition and Image Processing, 203-224, 1977.